The invention relates generally to reinforced plastic containers and more specifically to a reinforced plastic container with a heating element integrally bonded in the container's interlaminate structure and the method of making the same. The invention will be disclosed, by way of example, in connection with a reinforced fiberglass tank of the type commonly used in the chemical and food processing industries. The tank of the preferred embodiment has a heating element integrally bonded between a corrosion barrier and a support layer or lamina in the composite laminate structure. The invention, however, relates more generally to containers and may be used for other types of containers, as for example fiberglass pipe, with integrally formed heating means.
The conventional method used in the past for heating fiberglass containers, as for example fiberglass tanks, has been to externally wrap a heating tape, of either polyester or TEFLON (TEFLON is a trademark of the E. I. DuPont Company of Wilmington, Delaware for polytetrafluoroethylene) containing an electrical resistance heating element, about the periphery of the container. When energized, the heating elements were operative to transfer heat to the container's contents, but only after transferring the heat through the thermal resistance of the entire container wall.
Another method of heating container contents has been to externally wrap an electrical heating blanket, usually formed of fiberglass or silicone, and to heat the container contents by again energizing the heating elements. In addition to the disadvantage of being required to transfer the heat through the container wall prior to heating the container contents, heating blankets are frequently difficult to apply or to wrap around a container.
Further difficulties with externally applied heating elements have resulted from nozzles or drains which are fastened onto containers as accessories and which interfere with the wrapped heating elements.
Additionally, many tanks are used outdoors and are frequently the objects of vandalism. When subjected to flying projectiles, as for example rocks and bullets, the externally applied heating systems experience failure. Often, damage to heating elements, which are occasionally covered by insulation on the peripheral sidewalls of the tank, necessitated the removal of all of the insulation material and the replacement of the entire heating system.
Secondary layups have also been used to apply heating elements to tanks. A heating element was placed or overlayed upon a surface of an otherwise completed or used tank and covered with resin in an attempt to cover the heating element and to secure it to the container. This overlaying, even when placed on the inside of the tank, resulted in a number of disadvantages. First, the new surface which was necessitated to cover the heating element was not molded. Thus, the resulting surface was not smooth and had diminish cleanability as compared to a molded surface. This last mentioned consequence takes special significance for containers used in certain industries, as for example the food industry, where even small imperfections in the surface may substantially increase the possibility of bacteria buildup. Further, secondary layups are inherently more difficult to bond and a real and active danger exists that the secondary layup will experience laminate shear or separation from the primary surface.
In the past, the disadvantages noted above were tolerated for lack of a better alternative. Applicant, however, has discovered a new and novel method of forming a reinforced plastic fiberglass container with an integral heating means that overcomes the disadvantages of the prior art. A heating element, according to the present invention, can now be placed in a container's interlaminate structure without deparating and without deleteriously affecting the physical properties and characteristics of the resulting structure.
Accordingly, it is an object of the present invention to provide a method of forming a fiberglass container with an internal molded surface adapted to interface with the container contents and having a heating element integrally formed in the container's interlaminate structure.
It is a further object of the present invention to provide a method of forming a fiberglass container in which a heating element is intimately positioned with respect to the contents to be heated.
It is another object of the present invention to provide a method of forming a heated fiberglass container which is energy efficient.
It is yet another object of the present invention to provide a method of forming a fiberglass container with a heating element formed in the interlaminate structure which does not reduce the structure's physical strength characteristics.
It is still another object of the present invention to provide a method of forming a fiberglass container with heating means which are guarded against vandalism.
It is still another object of the present invention to provide a method of forming a heating element which is bonded between a corrosion barrier and a structural layer of a container.
It is yet another object of the present invention to provide a method of forming a fiberglass container with high heating capabilities which cannot be damaged by overheating.
It is yet another object of the present invention to provide a method of forming a container with heating elements which do not interfere with auxiliary nozzles, drains, etc.
It is still another object of the present invention to provide a method of forming a container which permits accurate temperature measurement and control of the container contents.